Project description:Alveologenesis is the culmination of lung development and involves the correct temporal and spatial signals to generate the delicate gas exchange interface. Using a novel Wnt signaling reporter system, we have identified a Wnt-responsive alveolar epithelial sublineage arising during alveologenesis called the axin2+ alveolar type 2 cell or AT2Aaxin2. The number of AT2Aaxin2 sublineage cells increases substantially during late lung development, revealing a wave of Wnt signaling during alveologenesis. Transcriptome analysis, in vivo clonal analysis, and ex vivo lung organoid assays reveal that AT2sAaxin2s promote enhanced AT2 cellalveolar growth during generation of the alveolus compared to the overall AT2 population. Activating Wnt signaling in the AT2 lineage results in expansion of the AT2axin2 sublineageAT2s whereas inhibition of Wnt signaling inhibits AT2 cell development and shunts alveolar epithelial development towards the AT1 cell lineage. These findings reveal a novel epithelial sublineage that coordinates Wnt-dependent alveolar growthAT2 expansion required for lung alveologenesis
Project description:Wnt/β-catenin signaling regulates progenitor cell fate decisions during lung development and in various adult tissues. Ectopic activation of Wnt/β-catenin signaling promotes tissue repair in emphysema, a devastating lung disease with progressive loss of parenchymal lung tissue. The identity of Wnt/β-catenin responsive progenitor cells and the potential impact of Wnt/β-catenin signaling on adult distal lung epithelial progenitor cell function in emphysema, are poorly understood. Here, we used a TCF/Lef:H2B/GFP reporter mice to investigate the role of Wnt/β-catenin signaling in lung organoid formation. We identified an organoid-forming adult distal lung epithelial progenitor cell population characterized by a low Wnt/β-catenin activity, which was enriched in club and alveolar epithelial type (AT)II cells. To further characterize the lung epithelial populations with different Wnt activities, we perform microarray analysis using freshly isolated Wnthigh/low/negative lung epithelial cells to study their transcriptome, specially the enriched genes and signaling pathways in the Wnt low population related epithelial stem cell functions.
Project description:Alveolar formation increases the surface area for gas-exchange and is key to the physiological function of the lung. Alveolar epithelial cells, myofibroblasts and endothelial cells undergo coordinated morphogenesis to generate epithelial folds (secondary septa) within the saccules to form alveoli. A mechanistic understanding of alveologenesis remains incomplete. We found that the planar cell polarity (PCP) pathway is required in both alveolar epithelial cells and myofibroblasts for alveologenesis. Our studies uncovered a Wnt5a–Ror2–Vangl2 cascade that endows cellular properties and thus novel mechanisms of alveologenesis. This includes PDGF secretion from alveolar type I and type II cells, cell shape changes of type I cells and migration of myofibroblasts. All these cellular properties are conferred by changes in the cytoskeleton and represent a new facet of PCP function. These results extend our current model of PCP signaling from polarizing a field of epithelial cells to conferring new properties at subcellular levels to regulate collective cell behavior.
Project description:The lung alveolus is the primary site of gas exchange in mammals. Within the alveolus, the alveolar type 2 (AT2) epithelial cell population generates surfactant to maintain alveolar structure and harbors a regenerative capacity to repair the alveolus after injury. We show that a Wnt-responsive alveolar epithelial progenitor (AEP) lineage within the AT2 cell population is critical for regenerating the alveolar niche. AEPs are a stable lineage during alveolar homeostasis but expand rapidly to regenerate a majority of the alveolar epithelium after acute lung injury. AEPs exhibit a distinct transcriptome, epigenome, and functional phenotype with specific responsiveness to Wnt and FGF signaling that modulates differentiation and self-renewal, respectively. Importantly, human AEPs (hAEPs) can be isolated and characterized through a conserved surface marker and are required for human alveolar self-renewal and differentiation using alveolar organoid assays. Together, our findings show that AEPs are an evolutionarily conserved alveolar progenitor lineage essential for regenerating the alveolar niche in the mammalian lung.
Project description:The lung alveolus is the primary site of gas exchange in mammals. Within the alveolus, the alveolar type 2 (AT2) epithelial cell population generates surfactant to maintain alveolar structure and harbors a regenerative capacity to repair the alveolus after injury. We show that a Wnt-responsive alveolar epithelial progenitor (AEP) lineage within the AT2 cell population is critical for regenerating the alveolar niche. AEPs are a stable lineage during alveolar homeostasis but expand rapidly to regenerate a majority of the alveolar epithelium after acute lung injury. AEPs exhibit a distinct transcriptome, epigenome, and functional phenotype with specific responsiveness to Wnt and FGF signaling that modulates differentiation and self-renewal, respectively. Importantly, human AEPs (hAEPs) can be isolated and characterized through a conserved surface marker and are required for human alveolar self-renewal and differentiation using alveolar organoid assays. Together, our findings show that AEPs are an evolutionarily conserved alveolar progenitor lineage essential for regenerating the alveolar niche in the mammalian lung.
Project description:The lung alveolus is the primary site of gas exchange in mammals. Within the alveolus, the alveolar type 2 (AT2) epithelial cell population generates surfactant to maintain alveolar structure and harbors a regenerative capacity to repair the alveolus after injury. We show that a Wnt-responsive alveolar epithelial progenitor (AEP) lineage within the AT2 cell population is critical for regenerating the alveolar niche. AEPs are a stable lineage during alveolar homeostasis but expand rapidly to regenerate a majority of the alveolar epithelium after acute lung injury. AEPs exhibit a distinct transcriptome, epigenome, and functional phenotype with specific responsiveness to Wnt and FGF signaling that modulates differentiation and self-renewal, respectively. Importantly, human AEPs (hAEPs) can be isolated and characterized through a conserved surface marker and are required for human alveolar self-renewal and differentiation using alveolar organoid assays. Together, our findings show that AEPs are an evolutionarily conserved alveolar progenitor lineage essential for regenerating the alveolar niche in the mammalian lung.
Project description:Alveologenesis, the final stage in lung development, substantially remodels the distal lung, expanding the alveolar surface area for efficient gas exchange. Secondary crest myofibroblasts (SCMF) exist transiently in the neonatal distal lung and are critical for alveologenesis. However, the pathways that regulate SCMF function, proliferation, and temporal identity remain poorly understood. To address this, we purified SCMFs from reporter mice, performed bulk RNA-sequencing, and found dynamic changes in Hippo-signaling components during alveologenesis. We deleted Hippo effectors, Yap/Taz, from Acta2-expressing SCMFs at the onset of alveologenesis, causing a significant arrest in alveolar development. Using scRNA-seq, we identified a distinct cluster of cells in mutant lungs with altered expression of marker genes associated with proximal mesenchymal cell types, airway smooth muscle (ASM), and alveolar duct myofibroblasts (DMF). Using lineage tracing, we show that neonatal Acta2-expressing SCMFs give rise to adult DMFs and that Yap/Taz mutants have an increase of persisting DMF-like cells in the alveolar ducts. Our findings identify aberrant differentiation of neonatal lung myofibroblasts and demonstrate that Yap/Taz are critical for maintaining lineage commitment.
Project description:Alveologenesis, the final stage in lung development, substantially remodels the distal lung, expanding the alveolar surface area for efficient gas exchange. Secondary crest myofibroblasts (SCMF) exist transiently in the neonatal distal lung and are critical for alveologenesis. However, the pathways that regulate SCMF function, proliferation, and temporal identity remain poorly understood. To address this, we purified SCMFs from reporter mice, performed bulk RNA-sequencing, and found dynamic changes in Hippo-signaling components during alveologenesis. We deleted Hippo effectors, Yap/Taz, from Acta2-expressing SCMFs at the onset of alveologenesis, causing a significant arrest in alveolar development. Using scRNA-seq, we identified a distinct cluster of cells in mutant lungs with altered expression of marker genes associated with proximal mesenchymal cell types, airway smooth muscle (ASM), and alveolar duct myofibroblasts (DMF). Using lineage tracing, we show that neonatal Acta2-expressing SCMFs give rise to adult DMFs and that Yap/Taz mutants have an increase of persisting DMF-like cells in the alveolar ducts. Our findings identify aberrant differentiation of neonatal lung myofibroblasts and demonstrate that Yap/Taz are critical for maintaining lineage commitment.
Project description:Mammalian lung development requires coordinated gene regulation to drive lung bud formation, branching morphogenesis, proximal-distal patterning, and epithelial specification. While key transcriptional and signaling regulators are known, the epigenetic regulators are less well studied. Here, we identify the canonical BAF complex as essential for lung epithelial development. Complete loss of BAF complex causes failure of lung formation, and selective deletion of ARID1A leads to loss of distal patterning and reduced alveolar type 1 (AT1) cell differentiation, with emergence of a highly proliferative cell state defined by joint activation of YAP and WNT signaling and loss of BMP response. Epigenomic analyses demonstrate broad failure of cell type-specific enhancer activation. Notably, exogenous BMP4 rescues distal differentiation in embryonic murine lung organoids, while YAP and WNT signaling require functional BAF complex. These data demonstrate a requirement for BAF complex activity during lung epithelial development and reveal a surprising differential specificity between signaling pathways.
Project description:The adult lung alveolus is a flexible 3D structure composed of multiple epithelial, endothelial, and mesenchymal cell types. Two highly specialized alveolar type I (AT1) and type II (AT2) cells, derived from epithelial progenitors, form the inner lining of the alveolus. During alveologenesis, the increasing demand for epithelial cells to cover the surface of the expansive number of alveoli is met by proliferating progenitor cells. There is presently little information about the identity of this population, and the niche microenvironment that controls its proliferation. We show that during alveologenesis genetic inactivation of TGFreceptors in hedgehog-responsive, PDGFRa(+) mesodermal cells previously identified as secondary crest myofibroblasts or SCMF reduces their number, and depletes a unique pool of proliferative epithelial progenitors, without significantly impacting differentiation of cells existing the pool. SCMF are a source of both extracellular matrix and secreted trophic molecules and may thus constitute a key component of the epithelial progenitor niche during alveologenesis. Paralleling the mouse model, we found evidence of reduced proliferation of SFTPC(+) progenitors in lungs of human preterm infants who died with bronchopulmonary dysplasia or BPD. SCMF are a transient cell population, which are depleted at completion of alveologenesis, making them a unique stage-dependent niche mesodermal cell type in mammalian organs.